Display screen or portion thereof with a graphical user interface



The FIGURE is a front view of a display screen or portion thereof with a graphical user interface, showing my new design.

The outermost set of broken lines and the broken line showing of rounded shapes illustrate an electronic device and the broken line at the periphery of the FIGURE illustrates the display screen. None of the broken lines form part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 